git-gui: make config gui.warndetachedcommit a boolean

Signed-off-by: Bert Wesarg <bert.wesarg@googlemail.com>
Signed-off-by: Pat Thoyts <patthoyts@users.sourceforge.net>

lib/commit.tcl

@@ -263,7 +263,7 @@ proc commit_commitmsg {curHEAD msg_p} {
 	global is_detached repo_config
 	global pch_error
 
-	if {$is_detached && $repo_config(gui.warndetachedcommit)} {
+	if {$is_detached && [is_config_true gui.warndetachedcommit]} {
 		set msg [mc "You are about to commit on a detached head.\
 This is a potentially dangerous thing to do because if you switch\
 to another branch you will loose your changes and it can be difficult\

lib/option.tcl

@@ -157,6 +157,7 @@ proc do_options {} {
 		{i-0..99 gui.commitmsgwidth {mc "Commit Message Text Width"}}
 		{t gui.newbranchtemplate {mc "New Branch Name Template"}}
 		{c gui.encoding {mc "Default File Contents Encoding"}}
+		{b gui.warndetachedcommit {mc "Warn before committing to a detached head"}}
 		{s gui.stageuntracked {mc "Staging of untracked files"} {list "yes" "no" "ask"}}
 		} {
 		set type [lindex $option 0]